There are a lot of posts in this thread, and I didn’t feel like reading all fifteen pages. So excuse me if I re-state something that has already been said.
The word “pagan” comes from the Latin “paganus,” meaning “rural person.” Basically, it referrs to indiginous peoples, tribal peoples, and old folk traditions. And more importantly, the people who worship their own gods, as opposed to converting to Christianity.
In modern terms, a Pagan is anyone polytheistic. These can be broken down into “Paleopagans,” who have continued worship their old gods continuously (such as pacific islanders), and “Neopagans,” who have returned to the old ways after a long hiatus. An example of that would be the people in Scandinavia, whose ancestors were converted to Christianity about nine hundred years ago, but in the past hundred years, have gone back to Odin and Thor. Neopagans also include Wicca, which is a relatively new religion (less than a century), but loosely based on the old Celtic traditions. Neopaganism is usually updated to be practical in the modern age (the Earth is no longer flat, no more human sacrifices, stuff like that). There’s also Pagan Reconstructionism, which would includ modern-day Druids, Sumerians, Mayans, etc. These are the Neopagans who are trying to return to the old ways, based on historical and archeological data. So naturally, it’s not going to be an EXACT reconstruction, but they’ll try to get as close as possible.
As I said, any polytheistic belief system is considered Pagan. But there’s some diagreement as to whether or not this includes Hinduism, since the Hindu gods are emmanations of a single god – sort of like the Holy Trinity, except with way more than three.